Is it better to use a cap when using the hair tool to avoid the hair particles from entering the mesh?
Hair caps are usually used because they make controlling distribution of hair strands easier. In my experience vertex groups alone are not always ideal due to how hair children interpolate. A good example is around the things like ears or anything similar should should have a gap in hair emission, where you may have faces with some vertices set to generate hairs, and some space in-between that should not, with vertex groups alone, these partially weighted faces may still get interpolated hairs, but with a cap you can just delete them.

Hair caps may also have slightly different topology that the underlying mesh to control the emission of hairs (e.g. extra loops / edges along where you want a part to be can make the result better defined).

Due to limitations in the collision system for hair they can improve collision handling with some extra setup, see here: How do I stop hair particles going through the body and the head?